A successor communication system of the wideband code division multiplexing (WCDMA) system, the high speed downlink packet access (HSDPA) system, the high speed uplink packet access (HSUPA) system, and the like, that is, the long term evolution (LTE) system has been examined by the standardization organization of WCDMA: 3GPP, and a specification operation has been in progress.
As a wireless access system in the LTE system, the orthogonal frequency division multiplexing access (OFDMA) system is defined for a downlink, and the single carrier frequency division multiplexing access (SC-FDMA) system is defined for an uplink (for example, see Non-Patent Document 1).
The OFDMA system is a multicarrier transmission system in which a frequency band into a plurality of narrow frequency bands (subcarriers) and transmission is performed by sending data on the subcarriers.
According to the OFDMA system, the subcarriers are orthogonally aligned on a frequency axis closely to each other, so that high speed transmission can be realized and an increase in utilization efficiency of frequencies can be expected.
The SC-FDMA system is a single carrier transmission system in which the frequency band is divided for each user device UE (user equipment) and transmission is performed using different frequency bands among a plurality of user devices UE.
According to the SC-FDMA system, interference among the user devices UE can be easily and effectively reduced and fluctuation of transmission power can be reduced. Therefore, the SC-FDMA system is favorable in terms of lower power consumption of the user devices UE, expansion of coverage, and the like.
In the LTE system, both in the downlink and the uplink, communication is performed by allocating one or more resource blocks (RB) to the user device UE.
A base station device eNB determines to which user device UE a resource block is allocated among the plurality of user devices UE for each subframe (1 ms in the LTE system) (such a process is called “scheduling”).
In the downlink, the base station device eNB is configured to transmit a downlink data signal to a user device UE selected in the scheduling using one or more resource blocks.
Further, in the uplink, a user device UE selected in the scheduling transmits an uplink data signal to the base station device eNB using one or more resource blocks.
Note that the uplink data signal is transmitted through a physical uplink shared channel (PUSCH), and the downlink data signal is transmitted through a physical downlink shared channel (PDSCH).
Here, the uplink data signal may be called “PUSCH signal”, and the downlink data signal may be called “PDSCH signal”.
Further, as a successor communication system of the LTE system, an LTE-Advanced system (LTE system on and after Release 10) has been examined in 3GPP (for example, see Non-Patent Document 2).
In the LTE-Advanced system, performing “carrier aggregation” is agreed as a required condition. Here, the “carrier aggregation” means simultaneously performing communication using a plurality of carriers.
For example, when the “carrier aggregation” is performed in the uplink, a different carrier is used in each component carrier (hereinafter, CC). Therefore, the user device UE transmits an uplink signal (that is, an uplink data signal and an uplink control signal) using the plurality of carriers.
Further, when the “carrier aggregation” is performed in the downlink, a different carrier is used in each CC. Therefore, the base station device eNB transmits a downlink signal (that is, a downlink data signal and a downlink control signal) using the plurality of carriers.
In the uplink of the LTE system, as described above, the single carrier transmission system is used. Therefore, the uplink signal is transmitted in a continuous frequency band.
On the other hand, in the uplink of the LTE-Advanced system, transmission of the uplink signal in a discontinuous frequency band has been examined in the following case.
<Case 1>
When the “carrier aggregation” is performed, an uplink data signal is transmitted in different CCs.
<Case 2>
When the “carrier aggregation” is performed, an uplink data signal and an uplink control signal are transmitted in different CCs.
Note that the uplink control signal is a signal transmitted through the physical uplink control channel (PUCCH), and may be called “PUCCH signal”.
<Case 3>
An uplink data signal is transmitted in a discontinuous (that is, discrete) frequency band within a single carrier.
<Case 4>
An uplink data signal and an uplink control signal are transmitted in a discontinuous frequency band within a single carrier.
By transmitting the uplink data signal in the discontinuous (that is, discrete) frequency band like the above-described Cases 1 and 3, more flexible allocation of frequency bands becomes possible, and the communication efficiency in the uplink can be improved.
That is, there are typically a good quality frequency band and a poor quality frequency band due to influence of Fading and the like. When allocation of the discontinuous frequency band is performed, a good quality frequency band can be selected and allocated as the frequency band in which the uplink signal is transmitted. Therefore, the communication efficiency in the uplink can be improved.
Put another way, when only the allocation of a continuous frequency band is performed, it becomes difficult to select and allocate such a good quality frequency band. The communication efficiency in the uplink cannot be improved compared with the case where the allocation of the discrete frequency band is performed.
Further, by transmitting the uplink data signal and the uplink control signal in the discontinuous frequency band like the above-described Cases 2 and 4, processing in which an uplink control signal to be transmitted through the PUCCH is transmitted through the PUSCH or processing in which transmission of a part of the signals is stopped can be avoided.
By the way, when an uplink signal is transmitted in the above-described discontinuous frequency band, a problem of an increase in peak-to-average ratio (PAPR) occurs.
When the PAPR is increased, the user device UE transmits the uplink signal in a non-linear region of a power amplifier. Therefore, an interference power to an adjacent channel (to an adjacent frequency band) is increased.
To suppress the increase in interference power to an adjacent channel, the user device UE needs to incorporate a power amplifier having high linearity. However, it is not favorable for the system as a whole because it leads to an increase in cost and size of the user device UE.
Therefore, to avoid the above-described increase in cost and size of the user device UE, and to avoid the influence of the increase in PAPR, reduction of maximum transmission power in the user device UE has been examined. The reduction of maximum transmission power in this way is called “maximum power reduction (MPR)” (for example, see Non-Patent Document 3).
A value of the MPR is determined based on a transmission bandwidth of each block, a difference between frequencies of blocks, and the like when each of allocated discontinuous frequency bands is called “block”.
In addition, when the maximum transmission power is reduced in this way, there is a problem of a decrease in cell coverage of an uplink. Therefore, typically, a minimum required value is defined as the value of the MPR.
Further, defining a control signal has been examined, which notifies whether the user device UE has a capability to transmit an uplink signal to the base station device eNB in a discontinuous frequency band.
By defining the control signal, the base station device eNB can grasp that the user device UE does not have the capability to transmit an uplink signal in a discontinuous frequency band, and by a method applied to the user device UE, it becomes possible to allocate a frequency band in which the uplink data signal and the uplink control signal are to be transmitted.